Our solar system consists of an average star we call the sun, the planets Mecury,Venus,Earth,Mars,Jupiter,Saturn,Uranus,Neptune, and Pluto. It includes: the satellites of the planets; numerous comets,asteroids, and meteoroids; and the interplanetary medium. The Sun is the richest source of electromagnetic energy (mostly in the form of heat and light) in the solar system. The Sun's nearest known stellar neighbor is a red dwarf star called Proxima Centauri, at a distance of 4.3 light years away. The whole solar system, together with the local stars visible on a clear night, orbits the center of our home galaxy, a spiral disk of 200 billion stars we call the Milky way. The Milky Way has two small galaxies orbiting it nearby, which are visible from the southern hemisphere.

Our sun is a mainstream star with a diameter of 1.4 million km and an absolute magnitude of 4.73. Its core temperature is approximately 14.6 million kelvin. The average distance from the earth to the sun is approximately 149.6 million km and the suns light takes about 8 minutes to reach us. This light and warmth is the source of all life on earth. Because of its proximity to us the sun is the only star that astronomers can observe and research in detail. The study of events on the surface of the sun has made possible advances in atomic, nuclear and plasma physics. Observations of the sun's surface, also called the photosphere, with special filters show an ever changing surface punctuated by the appearances of sunspots, faculae, flares and protuberances. The sun exhibits differing rotational periods of between 24 and 34 days depending on the solar latitude. All surface phenomena rotate accordingly.

The Moon probably formed early in the formation of the Solar System when a planet perhaps as large as Mars hit the newly-formed Earth which threw out a cloud of gas and dust which eventually formed the Moon. As it formed it became hot and molten. As it cooled the crust formed. The Moon is not big enough to hold on to an atmosphere. Its gravity is too weak to stop molecules of gas escaping. Without an atmosphere any small meteorites which hit the surface do not burn up, but instead form small craters. Large ones form large craters. Large meteorite impacts created the mare basins (people originally thought they were seas, which is the meaning of mare). Volcanoes then filled these basins with dark basaltic lavas. Other areas of the Moon are higher than the basins. They are heavily cratered and lighter in color than the mare. They are called terra, meaning land. Most volcanic activity then stopped, at least 2,000 million years ago. Most of these lava-flooded mare occurred on one side of the Moon. This made the Moon heavier on one side than the other. This heavy side is attracted to the Earth and always faces it. This was one reason why the Greeks believed that things in the sky did not change, which helped them to believe that the changeable Earth was the center of the Universe. Recently water was discovered on the Moon .

The Mercury

Mercury is nearer to the sun than any other planet, so it is the hottest. It is also the smallest of the inner planets. Being small and near the Sun, Mercury is very hard to see with a telescope. Satellites show that its surface is mostly heavily cratered. The major feature is a huge impact crater with a diameter of 1,300 kilometers - a quarter of the diameter of the planet. There is also evidence of some long extinct volcanoes. Because it is so hot and small, Mercury could not keep any of the gases released by the volcanoes and now lies naked beneath the baking rays of the nearby Sun. It probably has a large iron core taking up most of the inside and creating a weak magnetic filed.

The Venus

The brightest of the planets, Venus can easily be seen as an evening and a morning star. It is the second planet from the sun. It is about the same size as the earth and has an atmosphere, giving it a bright appearance. The atmosphere consists mostly of carbon dioxide. The surface of the planet is very hot because of the greenhouse effect. Most of the surface consists of vast plains, but there are several large highland regions several kilometers high. There are recent impact craters and volcanoes , although no evidence has been found of any active ones.

The Mars

Mars is the fourth planet from the sun. Its most famous feature is its red color produced by rust. Mars is just over half the size of the Earth. It probably has an iron corn. There are several huge extinct volcanoes, the largest of which is Olympus Mons. These volcanoes probably released the water and carbon dioxide still found in the thin atmosphere which produces dust storms, clouds and mist. There is a thin ice cap at the poles, probably made of water ice and solid carbon dioxide. Channels on the surface indicate that liquid water once flowed on the surface of Mars. Mars has two small moons which are probably captured asteroids. It had long been thought that life might exist on Mars but satellite exploration has found no evidence for it. Some people think they can see evidence of cells in meteorits believed to have come from Mars.